Ultrasonic transducers are used in various applications. For example, such ultrasonic transducers are widely used in semiconductor packaging equipment such as automatic wire bonding machines (e.g., ball bonding machines, wedge bonding machines, ribbon bonding machines, etc.) and advanced packaging machines (e.g., flip chip bonding machines such as thermocompression bonding machines, etc.).
An exemplary conventional wire bonding sequence includes: (1) forming a first bond of a wire loop on a bonding location of a first semiconductor element (such as a semiconductor die) using a wire bonding tool; (2) extending a length of wire, continuous with the first bond, from the first semiconductor element to a second semiconductor element (or a substrate, such as a leadframe, supporting the first semiconductor element); (3) bonding the wire to a bonding location of the second semiconductor element (or the substrate), using the bonding tool, to form a second bond of the wire loop; and (5) severing the wire from a wire supply, thereby forming the wire loop. In forming the bonds between (a) the ends of the wire loop, and (b) the bond locations, ultrasonic energy provided by an ultrasonic transducer is utilized.
An exemplary flip chip bonding sequence includes: (1) aligning first conductive structures of a first semiconductor element (such as a semiconductor die) with second conductive structures of a second semiconductor element; (2) bonding the first semiconductor element to the second semiconductor element utilizing ultrasonic bonding energy (and perhaps heat and/or force) such that corresponding pairs of the first conductive structures and second conductive structures are bonded together (where solder material may be included in the interconnection between the first conductive structures and the second conductive structures).
U.S. Pat. No. 5,595,328 (titled “SELF ISOLATING ULTRASONIC TRANSDUCER”); U.S. Pat. No. 5,699,953 (titled “MULTI RESONANCE UNIBODY ULTRASONIC TRANSDUCER”); U.S. Pat. No. 5,884,834 (titled “MULTI-FREQUENCY ULTRASONIC WIRE BONDER AND METHOD”); U.S. Pat. No. 7,137,543 (titled “INTEGRATED FLEXURE MOUNT SCHEME FOR DYNAMIC ISOLATION OF ULTRASONIC TRANSDUCERS”); U.S. Pat. No. 8,251,275 (titled “ULTRASONIC TRANSDUCERS FOR WIRE BONDING AND METHODS OF FORMING WIRE BONDS USING ULTRASONIC TRANSDUCERS”); and U.S. Pat. No. 9,136,240 (titled “SYSTEMS AND METHODS FOR BONDING SEMICONDUCTOR ELEMENTS”) relate to ultrasonic transducers and are herein incorporated by reference in their entirety. Ultrasonic bonding energy is typically applied using an ultrasonic transducer, where the bonding tool is attached to the transducer. The transducer typically includes a driver such as a stack of piezoelectric elements (e.g., piezoelectric crystals, piezoelectric ceramics, etc.). Electrical energy is applied to the driver, and converts the electrical energy to mechanical energy, thereby moving the bonding tool tip in a scrubbing motion.
In the use of such transducers, challenges exist when the mounting structure has a resonant frequency that coincides with (or is near) an operating mode of the transducer. Such challenges are particularly difficult with respect to ultrasonic transducers configured to operate at a plurality of frequencies. That is, while certain transducers may be optimized for operation at a first operating mode (e.g., a high frequency mode), the transducers may have issues with impedance stability at a second operating mode (e.g., a low frequency mode). For example, high impedance may result at the second operating mode, with the high impedance causing field issues (e.g., ultrasonic tuning failures).
It would be desirable to provide improved ultrasonic transducers for use in connection with various applications such as semiconductor packaging equipment (e.g., automatic wire bonding machines, advanced packaging machines, etc.).